Radar is used in many applications to detect target objects such as airplanes, military targets, vehicles, and pedestrians. Radar finds use in a number of applications associated with a motor vehicle such as for adaptive cruise control, collision warning, blind spot warning, lane change assist, parking assist and rear collision warning. Pulse radar or Frequency-Modulated Continuous-Wave (FMCW) radar are conventionally used in such applications.
In a radar system, a local oscillator (LO) generates a transmit signal. A voltage controlled oscillator (VCO) converts a voltage variation into a corresponding frequency variation. The transmit signal is amplified and transmitted by one or more transmit units. In FMCW radar, the frequency of the transmit signal is varied linearly with time. This transmit signal is referred as a ramp signal or a chirp signal. One or more obstacles scatters (or reflects) the transmit signal which is received by one or more receive units in the FMCW radar system.
A baseband signal is obtained from a mixer which mixes the transmitted LO signal and the received scattered signal that is termed an intermediate frequency (IF) signal. The IF signal is signal conditioned by a conditioning circuit which includes an amplifier and an anti-alias filter, is sampled by an analog to digital converter (ADC), and then is processed by a processor (e.g., microprocessor) to estimate a distance and a velocity of one or more nearby obstacles that provide scatter. Each peak in the fast Fourier transform (FFT) of the digitized IF signal corresponds to an object. The frequency of the IF signal is proportional to the range (distance) of the obstacle(s).
77 GHz automotive radar is a fast-growing market segment, with a variety of existing and emerging applications. For example, the frequency of the transmitted chirp signal may be controlled to increase at a constant linear ramp rate from 77 GHz to 81 GHz in a period of about 100 microseconds. FMCW modulation is the preferred radar choice due to its various advantages including a large RF sweep bandwidth (enabling high range resolution), while keeping the IF/ADC bandwidth small, and lower peak power consumption needed as compared to pulsed radar.
The signal processing for FMCW radar systems (such as for advanced driver assist systems (ADAS)) is typically performed using a radar micro controller unit (MCU). The radar MCU generally includes a FFT hardware accelerator and a lock-step safety central processing unit (CPU) for object detection and tracking.
FMCW radar signal processing involves generating what is termed three (3) dimensions including the computation of a first-dimension (range) FFT, second-dimension (Doppler) FFT and third-dimension angle-of-arrival estimation processing (beamforming). An advantage of using a fast (saw-tooth) FMCW radar waveform is that it can provide a two-dimensional range-velocity view of the objects illuminated by the radar, and additionally, the angle-of-arrival can be obtained through the use of multiple TX/RX antennas using digital beamforming.